Element for electromagnetic shielding and method for manufacturing thereof

ABSTRACT

A method for manufacturing an element for electromagnetic shielding. The method is characterized by the steps of arranging, along a curve corresponding to the extension of the completed element, a viscous material in the form of a bead, and orienting the particles in the material by applying a magnetic field across the bead. The material carries particles with substantial electrical conductivity and also ferromagnetic and/or ferrimagnetic properties. Also disclosed are a corresponding element for electromagnetic shielding, a device for electromagnetic shielding including such an element, use of such an element in a mobile phone and at a base station, and also a mobile phone and a base station including such an element.

FIELD OF THE INVENTION

The present invention relates to an element for electromagneticshielding, a method for manufacturing thereof and a device comprisingsuch an element. More specifically, the invention concerns such anelement for electromagnetic shielding, comprising an elastic materialwhich carries particles with substantial electrical conductivity.

BACKGROUND ART

For expedient function, electronic-equipment must, usually be shieldedfrom electromagnetic radiation. The equipment may also comprisecomponents which themselves generate electromagnetic radiation that mustbe shielded.

To provide such shielding, the electronic equipment, or its components,is normally enclosed in casings with electrical conductivity, whichconsequently act as a Faraday cage.

To allow access to the electronic equipment or its components, thesecasings are usually made to be opened, in which case elastic elements ofthe type described by way of introduction are used to ensure thenecessary shielding.

Such an element is known from, for example, GB 2049718. The elementdescribed comprises an elastic, electrically non-conductive materialwhich carries electrically conductive flakes. The flakes are oriented toincrease the conductivity of the element in a certain direction. Toachieve this orientation, the material, when still viscous, is subjectedto a shearing process, which can be effected by extrusion. Subsequently,the material is allowed to cure, after which the material is sliced in adirection which is preferably perpendicular to the direction ofextrusion. The completed element is finally punched from the slices ofmaterial. Although the thus manufactured elements for electromagneticshielding have an advantageous conductivity in a desired direction, theyare difficult to manufacture and besides it is difficult to provide morecomplicated designs of the elements.

Moreover, a casing with an elastic element of the type described by wayof introduction is known from, for example, U.S. Pat. No. 5,882,729.

The element described in the above publication is manufactured bydispensing a viscous material carrying particles with substantialelectrical conductivity on a housing. The viscous material is dispensedin the form of a bead of the required extension, after which thematerial is treated to assume an elastic, non-viscous state. The elementensures good electric contact between the housing and a cover when thisis closed and caused to abut against the element.

A problem with elements of this type is that the particles that providethe electrical conductivity of the element are relatively expensive. Itwould therefore be desirable to reduce the amount of particles which isincluded in the element.

Furthermore, for dispensing to be possible, the material must have arelatively low viscosity. As a result, the dispensed bead will have ashape corresponding to a lying D.

A thus designed element requires a relatively high compression force toachieve the necessary electric contact between, for instance, a housingand a cover.

In many fields, it is required that the electronic equipment be madeincreasingly smaller. For instance, there is an ongoing developmenttowards manufacture of smaller, thinner and lighter mobile phones.Unnecessarily high compression forces may in this context causedeformation of the casing of the mobile phone.

Also in shielding covers for base stations for mobile telephony there isa need for lowered compression forces in shielding elements, since thenow prevailing relatively high compression forces require expensivestiffeners and/or great wall thicknesses.

There is thus a need for elements that require lower compression forces.The solution suggested in U.S. Pat. No. 5,882,729 is dispensing of aplurality of beads, thereby building a vertically tapering element. Itwill be appreciated that this is a complicated and time-consumingprocess which has a detrimental effect on the cost of manufacture of theelement.

A further method of making thus tapering elements is injection moulding,but this is not a practically applicable method for surface-sensitive orlarge components.

Finally it is known from U.S. Pat. No. 4,778,635 to make a material withanisotropic electrical conductivity by subjecting a viscous material,which carries electrically conductive particles, to a spatially varyingmagnetic field while at the same time the material cures. Morespecifically, the varying magnetic field affects the particles so thatthey are concentrated in beads whose positions are locked as thematerial cures.

SUMMARY OF THE INVENTION

In view of the above, an object of the present invention is to providean improved element for electromagnetic shielding and a correspondingmethod for manufacturing thereof.

Another object is to provide an improved device for electromagneticshielding comprising such an element.

The element should preferably have good electrical conductivity in spiteof a reduced particle content.

The element should also preferably require a reduced compression force.

To achieve these objects, and also other objects that are evident fromthe following description, a method is provided according to the presentinvention for manufacturing an element for electromagnetic shielding, adevice for electromagnetic shielding, an element for electromagneticshielding, use of an element, a mobile phone, and a base station.

More specifically, according to the present invention a method isprovided for manufacturing an element for electromagnetic shielding,which method is characterised by the steps of arranging a viscousmaterial in the form of a longitudinally extended bead, the materialcarrying particles with substantial electrical conductivity andferromagnetic and/or ferrimagnetic properties, and orienting theparticles in the material by applying a magnetic field across said bead.

By the term viscous material which is used above and in the following ismeant a sticky, viscous material. Such a material can, for instance at ashear rate of 10⁻¹ s, have a viscosity in the range 30–300 Pas.

This results in an improved method for manufacturing an element forelectromagnetic shielding. Owing to the fact that the particles areoriented by applying a magnetic field, the electrical conductivity ofthe element is improved. More specifically, the particles will bearranged in rows along the field lines of the magnetic field. It willthus be possible to provide a given conductivity with a reduced amountof particles. Since the cost of said particles constitutes a main partof the total cost of material for the element, this reduced need forparticles results in a considerable saving in costs. An element with areduced particle content requires also a lower compression force. Thereason is that the particles act to reinforce the material of theelement. Thus, a reduced particle content results in reducedreinforcement.

The inventive method comprises advantageously also the step of treatingthe bead in such a manner that the material assumes an elastic,non-viscous state, whereby the particles are fixed with maintainedorientation. Advantageously the material is selected from the groupconsisting of silicone rubber, polyurethane and TPE (i.e. thermoplasticelastomer). If the material is silicone rubber, the material is treatedby a curing process, whereby it assumes an elastic, nonviscous statewhile the particles are fixed with maintained orientation.

According to a preferred embodiment of the inventive method, themagnetic field applied across the bead is given such a strength and/orduration that the particles, during their orientation in the samedirection as the magnetic field, affect the geometry of the bead. Themagnetic field is advantageously directed so that the particles, duringtheir orientation, affect the material of the bead in such a manner thatthe bead assumes a geometry tapering from a base towards an apex. A thusdesigned element requires a reduced compression force.

According to another preferred embodiment, the magnetic field appliedacross the bead is given such a strength and/or duration that aconcentration of particles is provided in the surface layer of the bead.In some cases, it is in fact in the surface of the element that the needfor substantial electrical conductivity is at its greatest. The magneticfield treatment thus makes it possible to ensure that the requisiteconductivity is provided in said surface layer while the particlecontent of the other parts of the material can be brought to a minimum.This means that the particle need may be further reduced, which has apositive effect on the manufacturing cost as well as the requiredcompression force.

According to yet another preferred embodiment of the present invention,said bead is made by a dispensing process. Alternatively, the bead canbe made by a screen-printing process.

The material is advantageously arranged in the form of a bead on asubstrate and is arranged for adhesion thereto. The magnetic field isadvantageously directed so as to act perpendicular to and in a directionaway from the surface of the substrate, on which surface the material isarranged.

The magnetic field applied across the bead preferably has a flux densityin the range 0.01–1 Tesla.

The particles are preferably formed so as to contain a ferromagneticmaterial such as iron, nickel, cobalt, or an alloy containing one ormore of said ferromagnetic materials.

The particles are preferably also formed with an outer layer of amaterial having substantial electrical conductivity.

The outer layer preferably forms also an oxidation inhibitor for aferro- and/or ferromagnetic material arranged inside the outer layer.

Furthermore, according to the present invention a method is provided formanufacturing an electromagnetic shielding element, which method ischaracterised by the steps of arranging, by a dispensing process, a beadof a viscous material, such as silicone rubber, and particles carriedtherein and having substantial electrical conductivity and ferro- and/orferromagnetic properties on a substrate, orienting the particles carriedby the material by applying a magnetic field across the bead, themagnetic field being directed so as to act perpendicular to thesubstrate in a direction away from the surface of the substrate, onwhich surface said bead is arranged, and treating the material so as toassume an elastic, non-viscous state.

Further a device for electromagnetic shielding is provided, comprisingan element made according to the method as described above.

According to the invention, also an element for electromagneticshielding is provided, comprising an elastic material which carriesparticles with substantially electrical conductivity, which element ischaracterised in that the particles are oriented in the material.

Thus, an element is provided which has extremely good electricalconductivity in relation to particle content. To achieve a givenconductivity, it will thus be possible to reduce the particle content,which has a positive effect on the manufacturing cost. Also the forcerequired for compressing the material is reduced.

According to a preferred embodiment of the element, said particles areoriented so that a concentration of particles is present in a surfacelayer of the material.

The material included in the element preferably consists of siliconerubber, polyurethane or TPE (i.e. thermoplastic elastomer).

According to another preferred embodiment, the particles have ferro-and/or ferrimagnetic properties. This makes it possible to achieve saidorientation of the particles by applying a magnetic field across theelement when its material is present in a viscous state. The particlesadvantageously contain nickel, iron, cobalt, or an alloy containing oneor more of these.

According to one more preferred embodiment, the particles have an outeroxidation-inhibiting layer with substantial electrical conductivity, theoxidation-inhibiting layer preferably containing silver.

According to another embodiment, the element has a shape tapering from abase towards an apex. This reduces the force required for compressingthe element.

According to one more embodiment, the elastic material also carriesparticles with substantial electrical conductivity and without ferro- orferrimagnetic properties.

According to the present invention, there are also provided use of anelement as described above for electromagnetic shielding in a mobilephone, and a mobile phone containing such an element.

Finally, according to the present invention, there are provided use ofan element as described above for electromagnetic shielding at a basestation, and also a base station containing such an element.

The present invention will now be described by way of example and withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an inventive shielding device with anelement for electromagnetic shielding.

FIG. 2 is a part-sectional perspective view of an element forelectromagnetic shielding in a state before its particles have beenoriented according to the present invention.

FIG. 3 is a schematic view of the process for orienting the particles inthe element shown in FIG. 2.

FIG. 4 is a cross-sectional view of an alternative embodiment of aninventive element for electromagnetic shielding.

FIG. 5 is a cross-sectional view of another alternative embodiment of aninventive element for electromagnetic shielding.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1, to which-reference is made, illustrates an inventive device 1for electromagnetic shielding.

The device 1 comprises a casing 2 with an opening 3 and a flange 4surrounding the opening 3. The casing 2 has substantial electricalconductivity and can thus be made of metal or metallised plastic. Thecasing 2 may also comprise a body without substantial conductivity, inwhich case a layer of substantial conductivity is applied to the innerand/or outer surface of the casing 2.

The device 1 further has an element 5, which is applied to thecircumferential flange 4 and has a shape tapering from a base towards anapex. The tapering shape means that the force required for compressingthe element 5, and thus providing good electric contact, is reduced.

The element 5 is made of an elastic material which carries particleswith substantial electrical conductivity. According to a preferredembodiment, the elastic material consists of silicone rubber while theparticles consist of nickel with an outer silver layer. The element 5and the method for manufacturing thereof will be described in moredetail below.

The device 1 for electromagnetic shielding can be used for shieldingelectronic equipment (not shown), such as a base station for mobiletelephony. The equipment is arranged in the casing 2 after which it isclosed with a suitably designed cover (not shown). The element 5 ensuresthat good electric contact is provided between the casing 2 and thecover.

The inventive device 1 can also be used for shielding of electronics inelectronic equipment such as one or more components on a printed circuitboard (not shown). The device 1 forms a casing 2 which is applied overthe group of components, the element 5 ensuring that good electriccontact between the casing 2 and the printed circuit board is provided.

The size of the inventive device 1 is of course adapted to the technicalfield in question.

It will be appreciated that the device 1 can also be configured in otherways. For example, it is possible to make the device 1 in the form of aframe which on opposite sides supports an element 5 for electromagneticshielding, which elements are in electric contact with each other. Theframe may then be used, for instance, as a spacer in a mobile phone,such as between two printed circuit boards or between a front and a backof the cover of the mobile phone.

FIG. 2, to which reference is now made, illustrates the appearance of aninventive element 5 during the manufacturing process.

A bead 6 of a viscous material 7, such as silicone rubber, is applied toa substrate 8 by a dispensing process, in which the material 7 isejected through a needle nozzle (not shown) which is advanced over thesubstrate 8 along a curve corresponding to the extension of thecompleted element 5. To ensure good adhesion between the bead ofmaterial 6 and the substrate 8, a primer can be applied to the substrate8 before dispensing of the bead 6.

For such a dispensing process to be allowed, the material 7 must have arelatively high viscosity, whereby the material 7, owing to gravity,will assume the shape of a lying D. Preferably the material has aviscosity in the range 30–300 Pas at a shear rate of 10⁻¹ s whenmeasuring in a rheometer Physica-Rheolab MC1 with a plate/platemeasuring system.

The material 7 carries particles 9 with substantial electricalconductivity and ferro- and/or ferrimagnetic properties.

According to the preferred embodiment, the particles 9 consist of nickelwith an outer silver layer. Nickel is ferromagnetic while the silverlayer acts as an oxidation inhibitor for the nickel. The silver alsopromotes the improvement of the electrical conductivity of the particles9.

The particles are preferably spherical, round, needle-shaped orlump-shaped, such as irregular granules.

FIG. 3, to which reference is now also made, illustrates the next stepfor manufacturing the inventive element 5.

The magnetic field 10 is applied across the material 7 arranged in theform of a bead 6. The magnetic field 10 is directed so as to actperpendicular to the substrate 8 away from the surface 11 on which thematerial 7 is arranged. The Figure illustrates how the magnetic field 10is applied by means of an electromagnet 12. However, it will beappreciated that the magnetic field 10 can be provided in other ways.

Owing to the ferromagnetic properties of the particles 9, the particleswill be affected by the magnetic field 10 and orient themselves in thesame direction as the magnetic field 10. More specifically, theparticles 9 will be oriented in rows extended along the field lines ofthe magnetic field 10. The orientation of the particles in rows isclearly to be seen from the enlargement of a detail in FIG. 3.

The orientation of the particles is facilitated by their advantageousshapes stated above. In the FIGURES, the particles are needle-shaped inorder to clearly illustrate their orientation caused by the magneticfield.

The orientation of the particles 9 promotes improvement of theelectrical conductivity of the element 5. Owing to said magnetic fieldtreatment, it is thus possible to reduce the amount of particles 9 forproviding a given conductivity in the element 5. This means aconsiderable saving in costs. The reduced amount of particles 9 alsoimplies that the force required for compressing the element 5 is reducedsince the particles 9 cause a reinforcement of the material 7. It goeswithout saying that a reduced amount of particles 9 will result in asmaller reinforcement.

By a suitable adaptation of the flux density of the magnetic field 10 itwill be possible to cause the particles 9, during their orientation, toaffect the material 7 of the bead 6 in such a manner that the bead 6changes its geometry. It is evident from FIG. 3 how the bead 6 hasassumed an essentially triangular geometry with a shape tapering from abase 13 towards an apex 14. Thus the magnetic field 10 affects theparticles 9 so that the particles during their orientation in turn acton the material 7 and extend it in the vertical direction.

The magnetic field has a field strength preferably in the range 0.01–1Tesla.

Subsequently the material 7 is treated in a suitable manner to make itassume an elastic, non-viscous state, whereby the particles 9 are fixedwith maintained orientation. If the material 7 consists of siliconerubber, this is subjected to a conventional curing process.

In a practical experiment, a bead 6 of silicone rubber was dispensed ona substrate 8. The silicone rubber carried particles 9 in the form ofnickel with an outer silver layer. The particles had a diameter in therange 10–100 μm, average diameter 40 μm. The bead 6 assumed essentiallythe shape of a lying D, width 1.3 mm and height 0.8 mm. Then a magneticfield 10 with a magnetic flux density of 0.05 Tesla was applied acrossthe bead 6 for 15 s in the manner as described above. The bead 6 therebyassumed a triangular shape with a height of 1.3 mm.

According to the present invention, an element 5 for electromagneticshielding and also a method for manufacturing thereof are provided. Theelement 5 comprises an elastic material 7 which carries orientedparticles 9 with substantial electrical conductivity. Owing to theorientation of the particles 9, the element 5 can be made to have agiven conductivity in spite of a reduced particle content. As a result,the manufacturing cost for the element 5 is lowered while at the sametime the necessary compression force can be reduced. Said orientation isprovided according to the present invention by applying a magnetic field10 across a bead of the material 7 when in a viscous state. Inconnection with the orientation of the particles 9 it is also possibleto affect the geometry of the bead 6.

According to a preferred embodiment of the inventive method, the bead ofmaterial can be arranged directly on a substrate and be arranged foradhesion thereto. The substrate may consist of a flange 4 of the casingshown in FIG. 1. However, other types of substrate are conceivable, suchas a frame structure which is intended to be arranged between twoelectrically conductive structures in the form of printed circuitboards.

According to another embodiment (not shown), also particles withsubstantial electrical conductivity are carried by the material of theelement. These electrically conductive particles help to electricallyconnect the particles with electrical conductivity as well as ferro-and/or ferrimagnetic properties when these are arranged in rows alongthe field lines of the magnetic field applied across the bead. Thisimproves the electrical conductivity of the element still more.

The present invention is extremely useful in the mobile phone industry.There is a strong downward pressure on prices of mobile phones andtherefore all savings in cost are of benefit to the manufacturers.Besides, the fact that the required compression force of the element 5can be reduced means that the element 5 itself does not constitute a barto designing smaller, lighter and thinner mobile phones.

The present invention is also very useful in shielding covers for basestations for mobile telephony. The reduced compression force of theinventive shielding element renders it possible to make the shieldingcover with a reduced wall thickness and/or without stiffeners.

It will be appreciated that the present invention is not restricted tothe embodiments described above.

For instance, it is conceivable to adjust the magnetic field 10 so thata concentration of particles 9 is provided in the surface layer 15 ofthe element 5, as shown in FIG. 4. The magnetic field 10 is adjusted interms of strength and duration, whereby a great amount of the particles9 is “extracted” from the material 7 and concentrated in its surfacelayer 15. A thus manufactured element 5 has extremely good electricalconductivity in the surface layer 15. This enables a further reductionof the amount of particles 9 in the material 7.

It is also conceivable to adjust the magnetic field 10 so that merely anorientation of the particles 9 is provided. The magnetic field 10 isgiven a relatively small strength, whereby the particles 9 during theirorientation are not capable of affecting the geometry of the bead,-whichis shown in FIG. 5.

Nor does the elastic material have to be arranged in the form of a beadby a dispensing process. For example, it is possible to provide thisbead by a screen-printing process.

It will also be appreciated that the elastic material included in theelement need not necessarily consist of a silicone rubber. Thus it isalso possible to manufacture the inventive element from other elasticmaterials, such as polyurethane, TPE (i.e. thermosplastic elastomer) orthe like.

The element 5 can further be given a complex geometric configuration. Toachieve this, it is possible, for instance, to dispense theparticle-carrying material on a non-planar substrate, i.e. a substrateextending in three dimensions.

Finally, it will also be appreciated that the particles can be designedin a way other than that described above. The particles advantageouslycontain a material with ferromagnetic properties. Non-limiting examplesof such materials are iron, nickel, cobalt, and alloys containing one ormore of these materials. The particles may also contain materials withferrimagnetic properties, in which case the particles preferably alsocontain an outer layer with substantial electrical conductivity sinceferrimagnetic materials normally have lower electrical conductivity. Asdescribed above, however, also particles containing ferromagneticmaterial may have such an outer layer with substantial electricalconductivity. This may be required in the cases when the ferromagneticmaterial has a tendency to oxidation which deteriorates the electricalconductivity of the material.

Several modifications and variations are thus conceivable, and thereforethe scope of the present invention is exclusively defined by theappended claims.

1. A method for manufacturing an element for electromagnetic shielding,comprising the steps of: arranging, along a curve corresponding to theextension of the element, a viscous material having a first externalshape, the viscous material carrying particles with substantialelectrical conductivity and at least one of ferromagnetic andferrimagnetic properties, and orienting the particles in the visciousmaterial by applying a magnetic field across said viscous material,wherein the magnetic field applied across the viscous material is givensuch a strength or duration that the particles, during their orientationin the same direction as the magnetic field, at least change the firstexternal shape of the viscous material into a second external shape. 2.A method as claimed in claim 1, wherein the step of orienting theparticles is followed by the step of treating the viscous material insuch a manner that the viscous material assumes an elastic, non-viscousstate, wherein the particles are fixed with maintained orientation.
 3. Amethod as claimed in claim 1, in which the magnetic field is directed sothat the particles, during their orientation, affect the viscousmaterial in such a manner that the viscous material assumes a shapetapering from a base towards an apex.
 4. A method as claimed in claim 1,in which the magnetic field applied across the viscous material is givensuch a strength or duration that a concentration of particles isprovided in the surface layer of the viscous material.
 5. A method asclaimed claim 1, in which said first external shape of the viscousmaterial is made by a dispensing process.
 6. A method as claimed inclaim 1, in which said first external shape of the viscous material ismade by a screen-printing process.
 7. A method as claimed in claim 1, inwhich the viscous material is arranged in the form of a bead on asubstrate and arranged for adhesion thereto.
 8. A method as claimed inclaim 1, in which the viscous material is arranged in the form of a beadon a substrate, the magnetic field being directed so as to actperpendicular to and in a direction away from the surface of thesubstrate, on which surface the material is arranged.
 9. A method asclaimed in claim 1, in which the magnetic field applied across theviscous material has a flux density in the range of 0.01–1 Tesla.
 10. Amethod as claimed in claim 1, in which said viscous material is selectedfrom the group consisting of silicone rubber, polyurethane andthermoplastic elastomer (TPE).
 11. A method as claimed in claim 10, inwhich the step of orienting the particles is followed by the step oftreating the viscous material by a curing process, wherein the viscousmaterial assumes an elastic, non-viscous state while the particles arefixed with maintained orientation.
 12. A method as claimed in claim 1,in which the particles are formed so as to comprise a ferromagneticmaterial including iron, nickel, cobalt or an alloy containing one ormore of said ferromagnetic materials.
 13. A method as claimed in claim1, in which the particles carried by the viscous material are formedwith an outer layer of a material with substantial electricalconductivity.
 14. A method as claimed in claim 1, in which the particlescarried by the viscous material are formed with an outer layer whichforms an oxidation inhibitor for a ferro- or ferrimagnetic materialarranged inside the outer layer.
 15. A device for electromagneticshielding, comprising an element manufactured according to the method asclaimed in claim
 1. 16. An element for electromagnetic shieldingmanufactured in accordance with the method of claim 1, comprlslng: anelastic material carrying parties with substantial electricalconductivity wherein the particles are oriented in the material alongfield lines of a magnetic field applied across the element and theelement has a shape tapering from a base towards an apex.
 17. An elementas claimed in claim 16, in which said particles are oriented so that aconcentration of particles is present in a surface layer of thematerial.
 18. An element as claimed in claim 16, in which the materialconsiste of silicone rubber, polyurethane or thermoplastic elastomer(TPE).
 19. An element as claimed in claim 16, in which the particleshave at least one of ferro- and ferrimagnetic properties.
 20. An elementas claimed in claim 19, in which the particles comprise nickel, iron,cobalt or an alloy containing one or more of these.
 21. An element asclaimed in claim 16, in which the particles have an outeroxidation-inhibiting layer with substantial electrical conductivity. 22.An element as claimed in claim 21, in which the oxidation-inhibitinglayer contains silver.
 23. An element as claimed in claim 16, in whichthe elastic material also carries particles with substantial electricalconductivity and without ferro- or ferrimagnetic properties.
 24. Amobile phone, comprising an element for electromagnetic shieldingaccording to claim
 16. 25. A base station for mobile telephony,comprising an element according to claim
 16. 26. An element as claimedin claim 17, in which the material consists of silicone rubber,polyurethane or thermoplastic elastomer (TPE).
 27. A method as claimedin claim 1, wherein said magnetic field affects and orients saidparticles.
 28. A method for manufacturing an electromagnetic shieldingelement, comprising the steps of: arranging on a substrate, by adispensing process and along a curve corresponding to the extension ofthe element, a length of a viscous material, including a siliconerubber, and particles carried therein and the particles havingsubstantial electrical conductivity and at least one of ferro- andferrimagnetic properties, orienting the particles carried by thematerial by applying a magnetic field across the the viscous material,the magnetic field being directed so as to act perpendicular to thesubstrate in a direction away from the surface of the substrate, onwhich surface said viscous material is arranged, wherein the magneticfield applied across the viscous material is given such a strength orduration that the particles, during their orientation in the samedirection as the magnetic field, at least change a first external shapeof the viscous material into a second external shape, and treating theviscous material so as to assume an elastic, non-viscous state.
 29. Amethod as claimed in claim 28, wherein said magnetic field affects andorients said particles.